Olivia Wilde and Hugh Laurie, <i>House</i> Olivia Wilde and Hugh Laurie, House

There's no denying that Monday's House is special — but not because it's the show's 150th episode.

"I refuse to acknowledge those numbers as milestones," creator and executive producer David Shore tells TVGuide.com. "I hate to pooh-pooh this, but I believe Episode 149 should be just as good as Episode 150. One number's not more important than another number. This is kind of a departure episode, but that's purely coincidental."

Mega Buzz: Clues about Thirteen's return to House

Whether or not all episodes are created equal, this hour (8/7c on Fox) is emotionally significant, both for Dr. House (Hugh Laurie

) and Thirteen (Olivia Wilde), who returns to the show after a mysterious disappearance more than a year ago. And since House and Thirteen's happy reunion takes place outside a New Jersey correctional facility, her return promises to be just as baffling.To say anything about why Thirteen ended up in the pokey is to say too much, but the secret will be revealed before the episode is over. Suffice to say the reason is very personal and extremely emotional, even for Dr. Crankypants, who is battling with his own recent breakup from Cuddy (Lisa Edelstein). "It's two people struggling with what to do with the past," Shore says. "In very subtle ways and sometimes not so subtle ways, it does change the nature of their relationship. This does serve as a bonding moment — a connecting moment."

Check out photos of the House cast

House even goes so far as to makes Thirteen an enormous promise — which, for him, represents a kindness rarely seen. "It's our version of a sweet gesture," Shore says with a laugh. But don't expect Princeton Plainsboro to become the warm and fuzzy zone. "That moment at the end is a significant moment," Shore says. "House is not an automaton; House is a human being. But the nature of this show is little, tiny, baby, baby steps. [He] steps forward in tiny little reveals, tiny little cracks and then just runs away from it as quickly as he can."How will the rest of the team react to Thirteen's return? Namely, will they, like House, be begging to learn her secret? "I'm not going to tell you it becomes a major brouhaha... [but] there's curiosity about her departure," Shore says. "This episode is all about, 'What is her secret? What is her secret?' Which is compelling the first time, but once we reveal the answer, we have no interest in repeating the arc.  But other people will find out her secret with interesting results in upcoming episodes."

Exclusive: Why House is unlikely to end up at NBC

And will those episodes be the show's last? Fox and NBC Universal, which produces the show, have yet to close a deal to guarantee future seasons of the show. Shore isn't worried. "I did not plan the ending [of the season] with a parachute in mind. I expect us to be back next year," he said. "I would be absolutely astounded if there wasn't [a Season 8]."

Are you happy to have Thirteen back? What do you think her secret is?